I'm just messing... I agree, almost everyone just saunters into the scene. But maybe the reason Thanos didn't attack was because he was surveying the scene and trying to figure out what's going on himself? I don't know... I can't defend that, nor do I want to.

But, I will say that my 8 year-old said he was fighting back tears during that scene (he eventually broke when Iron Man died) and my 6 year-old stood up and did a fist pump in the air when Spider-man came through (he was devastated after Infinity War specifically because of Spider-man). So yes, adult me would side with your gripes. But at the same time, it's just a dope moment.